Belt Squeals When AC Is On – Reasons and Fixing

If a belt squeals when AC is on in your car, that’s a symptom of a faulty component in the Air conditioning system. Therefore, it is crucial to find out the cause of the occurrence and fix it as soon as possible.

Belt squeals, when the AC is on, are a telltale symptom indicating tension issues within a vehicle’s drive belt system. These squeals, often described as a sharp, persistent sound, typically emerge from the drive belts as they lose grip on the pulleys. The main cause is usually a decrease in tension or wear on the drive surface of the air conditioning compressor belt.

Over time, belts may stretch beyond their effective span, leading to deflection and slippage. Regular diagnosis is essential to avoid such issues, ensuring belts maintain proper tension through spring-loaded tensioners, thus prolonging the lifespan of the drive system and preventing belt squealing.

Meanwhile, this article unveils the details causes of belt squeals when AC is on and how to rectify the issue. So why not take a moment to digest such valuable information below?

belt squeals when ac is on

What does the AC Belt do?

An AC belt, also known as an air conditioning belt or serpentine belt, is responsible for driving the air conditioning compressor in a car. The compressor is a critical component of the car’s air conditioning system. Here’s what the AC belt does:

  1. Drives the Compressor: The AC belt connects to the car’s engine and powers the AC compressor. The compressor is essential for circulating refrigerant through the air conditioning system, enabling it to cool the air.
  2. Transfers Power: When the engine is running, the AC belt transfers mechanical power from the engine to the compressor. This process allows the compressor to compress and circulate the refrigerant.
  3. Facilitates Cooling: By driving the compressor, the AC belt helps maintain the refrigerant’s flow, which is crucial for the air conditioning system to produce cold air and maintain a comfortable cabin temperature.

If the AC belt breaks or becomes worn, the air conditioning system will not function properly, and the vehicle interior will not be cooled effectively. Regular maintenance and timely replacement of the AC belt are important to ensure the AC system operates efficiently.

Causes of Belt Squeals When AC Is On

An ac belt squealing can generate a loud, frustrating noise if you fail to rectify the issue immediately. However, it is vital to know the cause of the problem before trying to figure out a solution.

So, if your AC belt squeals when you turn on your car’s air conditioning system, the following may be the cause like worn and loose serpentine belt or bad ac compressor.

A loose or worn serpentine belt

The serpentine belt is designed to power a vehicle’s alternator, power steering pump, water pump (in some cars), and the air conditioner’s compressor. The component kicks in and transmits rotational energy to these components when a car is running.

The belt is also called a drive belt because it drives multiple peripheral parts in an automobile’s engine. Usually, when you turn on your car’s air conditioning system, the AC compressor is automatically engaged.

Once this occurs, the load is placed on the serpentine belt and the car’s engine. Over time, the grooves on the serpentine belt that enables it to engage the pulley’s grooves wear out gradually due to friction.

After a while, the drive belt becomes worn out and unable to fit into the grooves on the pulley as expected. This loose fit will eventually result in a loud squealing noise as the AC continues to work. If you hear noise when AC is on in a car or blows smoke, kindly check it out and fix it ASAP.

A cracked or broken drive belt

The experience is somewhat similar to the one above. A broken serpentine or drive belt will produce a loud ac belt squeaking or slapping noise when you turn on the AC in your car.

Unfortunately, the problem doesn’t end with the air conditioner. A cracked serpentine belt will affect the proper functioning of a car’s alternator, water pump, and power steering pump.

In other words, a broken serpentine belt will result in a squealing noise, and lead to heavy steering, improper coolant circulation and engine overheating, etc.

Other Reasons for Squealing Noise of Car AC

Besides a worn-out or broken serpentine belt, some other issues may be responsible if your car’s drive belt squeals when AC is turned on. Some of the other issues include the following.

Faulty AC compressor clutch

The compressor clutch is responsible for engaging the compressor and pressurizing the entire air conditioning system to trigger the process that releases cold air. Unfortunately, this component can fail due to a bad clutch coil, a blown fuse, or poor ground.

When this happens, the AC will automatically release a loud squealing noise. Therefore, if you constantly hear this noise when you turn on your AC, verify whether you have a bad AC compressor.

Defective AC compressor pulley and bearing

The AC compressor pulley is the part of the air conditioning system that is connected to the serpentine belt. The component rotates as the serpentine belt transmits rotational energy when the engine runs.

The compressor pulley also features a bearing, which enhances its rotation. However, if these components become damaged over time, you will eventually hear a loud squealing noise when AC is turned on.

What Happens if AC Belt Breaks?

If the AC belt breaks, several issues can arise, primarily affecting the air conditioning system and potentially other components:

  1. Loss of Air Conditioning: The most immediate and noticeable effect is that the air conditioning system will stop working. Without the belt, the compressor cannot function, which means the refrigerant won’t circulate, and the system cannot produce cold air.
  2. Potential Impact on Other Systems: In some modern vehicles, the AC belt is part of the serpentine belt system, which also drives other accessories such as the alternator, power steering pump, and water pump. If the belt that breaks is the serpentine belt, it can lead to a loss of power steering, battery charging, and engine cooling, causing more significant problems.
  3. Increased Engine Temperature: If the serpentine belt powers the water pump and it breaks, the engine may overheat due to the loss of coolant circulation. It can cause severe engine damage if not addressed promptly.
  4. Dashboard Warning Lights: The breakage may trigger warning lights on the dashboard, such as the battery light (if the alternator is affected) or the engine temperature light.
  5. Reduced Vehicle Performance: Loss of power steering and alternator function can make the vehicle harder to drive and lead to a dead battery if the alternator is not charging it.

Regular maintenance and inspections can prevent AC belt breakage and ensure the smooth operation of your vehicle systems.

Can You Drive with a Broken AC Belt?

Driving with a broken AC belt depends on the specific design of your vehicle’s accessory drive system. Here are some considerations:

  1. Standalone AC Belt:
    • If the AC belt solely drives the air conditioning compressor and is separate from the serpentine belt system, you can continue driving the car. The main impact will be the loss of air conditioning, which may be uncomfortable in hot weather but does not affect the car’s overall functionality.
  2. Serpentine Belt System:
    • In many latest vehicles, the AC belt is part of a serpentine belt system that drives multiple accessories, including the alternator, power steering pump, and water pump. If this belt breaks, it can lead to several critical issues:
      • Loss of Power Steering: This makes the vehicle much harder to steer, especially at low speeds.
      • Loss of Alternator Function: This can cause the battery to drain, leading to electrical system failures and potentially leaving you stranded with a dead battery.
      • Loss of Water Pump Function: If not addressed promptly, this can cause the engine to overheat, leading to severe engine damage.

In the case of a broken serpentine belt, it is not advisable to continue driving, as it can cause significant damage to your vehicle and pose a safety risk.

How Do You Fix A Squeaky AC Belt?

Fixing a squeaky AC belt is pretty straightforward. Simply get a bottle of WD-40 and spray some of the content on the drive belt until you can’t hear the noise anymore. You can do this while the car’s engine is running to know when the noise ceases.

Also, you can use a bar soap if you don’t have a bottle of WD-40 handy at the moment. Simply rub the bar soap on the AC belt a couple of times. Please turn on the car to verify whether it stops the unpleasant squeaking noise.

Track and fix the leading cause of the problem if the soapy water did not fix it.  For example, if a loose or worn belt is the culprit, adjust or replace the belt to resolve the issue. If that is not the culprit, examine the compressor clutch and pulley. If the clutch is wobbling or the pulley teeth are bent or damaged, replace it.

Can I Put WD 40 On A Squeaky Belt?

WD-40 can silence the noise if your car squeaks when AC is on. However, in some cases, the fluid might weaken and break down your car’s serpentine belt. This is because WD-40 is a petroleum-based product.

 Therefore, you may want to apply any other method to stop the squeaky noise coming from your worn-out serpentine belt. For example, you can spray soapy water on the belt or use your common deodorant to stop the noise if your drive belt squeal when AC is on.

noise when ac is on in car

How Much Does It Cost To Fix A Squeaky Belt?

Fixing a squeaky belt costs around $100 – $195. The total cost comprises of $25 – $75 for parts and $75 – $120 for labor fees, respectively.

If your AC is making a screeching sound due to a bad serpentine belt, you can simply get the part from an auto parts shop across the street and fix it yourself in your garage (if you’re a DIYer).

 Of course, this will save you a whopping $75 – $120 labor cost. However, kindly contact an expert auto technician if you can’t handle it.


There’s no need to worry if your belt squeals when AC is on. It’s just a sign of a worn, loose, or broken serpentine belt. All you need to do is get any of the substances recommended above in this article to stop the noise.

However, if your AC compressor squeals on startup due to an excessively damaged AC belt, this might be the right time to replace the belt. Again, the parts and labor fee will only cost you a few bucks.

Solomon Osuagwu

Osuagwu Solomon is a vetted auto mechanic with over ten years of experience in the garage and five years of experience as a service writer. He prides himself in writing accurate information on professional repair guides, DIY repair guides, buyer’s guides, comparisons, and car reviews. If he’s not in his repair garage, he’s writing automotive blogs to help car owners and fellow mechanics to troubleshoot and proffer solutions to several car problems.

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